Method for purifying uranium



1958 J. w. KENNEDY ET AL 2,849,285

METHOD FOR PURIFYING URANIUM Original Filed June 26, 1944 FROM PREVIOUS L TREATMENT I V 5 11 VAPORS 2 I Fe f-l-f Pb 'l'f' H/VOJ 2 Sheets-Sheet 2 EVAPORATI N c 0/ AND OXIDIZING 3 SULFUR 1 Fe/0/19 ,Pb(0//) PRECI Z %(/v/1 0o AND FILTERING //v 311/ NHH v F/L T194 U02 {00 1 -4 v4 po/rs ACIDIFYINGI AND IGNITING 8/ 0 PFEC/P/TATE 5/02 DISSO LVI N G a AND FILTERING EVAPORATING AND IGNITING I'N TARED CONTAINER PURIFIED U308 INVENTORS JOSE H W/(f/i/A/[Dl AIT ORNE Y 2,849,285 Patented Aug. 26, 1958 7 METHOD FOR PUR IFYING URANIUM I Joseph W. Kennedy, Berkeley, Calif., and Emilio G.

Segre, Santa Fe, N. Mex., assignors to the United States of America as represented by theUnited StatesA'tomlc Energy Commission Original application June 26, 1944,.Se1'ial No. 542,220. gigigsg and this application July'21, 1945,'.Serial -'N.o.

2 Claims. (Cl. 23-445 This invention relates to the.purification .of. uranium,

and more particularly, to the preparation of uranium such a highly purified form that the method of determining the isotopic constituency of uranium according to the "procedure described and claimed in.-the copending applidivision of the copending application Serial No.,542,22 0,'

filed June 26, 1944, by JosephW; Kennedy andEmilio G. Segre, now abandoned.

Natural uranium comprises. three isotopes,-,.nam.ely,,

U U and U Thisis'true in. generalof Uranium obtained by treating natural uranium in anisotope enriching device, such as a calutronofihe type"described and claimed in the copending application Serial fNo.

557,784, filed October 9, 'l944,-' by Ernest O.' Lawrence,-

issued as Patent No. 2,709,222 on May 24, 1955i In'the method of analyzing uranium for the, polyisotopejcomprising the aforementioned three'uranium isotopes,iasfdescribed in application Serial No. 536,440,' three independent measurements are required. These are a measurement of the mass, a measurement of the .rate" of radio active disintegration or the alpha activity, and a measurement of slow-neutron-produced fission. I

In order to measure the true mass of the uranium which is analyzed, the uranium mustbe chemically jpurified and converted into a known compound,sothat"by weighing the compound and applying the appropriate gravimetric factor the true mass of the'uraniu'm in.the'. ':oxnp.mn l' can be determined. A suitable compound'forthis purpose i the oxide of uranium, U 0

In order to measure the trueir'ateof radioactive disintegration or the alpha activityof thefsampleoffuranium which is analyzed, care must'be' taken sothat the full count of alpha-particles resultingjfromi thedisintegration is obtained. If the sample of"uranium,"in the-form of U 0 which ismeasuredfor alpha activity is too thick,

some of the alpha-particles arisingfrom'the'disintegration of uranium atoms are unable to penetratethedhickness of the U 0 and are absorbed therein. The-alphaparticles which do not penetrate'the thickness of'f'the U 0 of course, are not counted by the devices'common- I 1y used for alpha activity measurements and; accordingly,

the full alpha activity is not measured. 'It willbe'understood that full count of;alpha-pa'rticles'andsimilarexpressions refer to the'emissi'on-of alpha-particles'from one face of the sample. In view of the absorption' efiect, it is necessary to prepare the, sample'of uraniumithat is to be subjected to analysis 'in the form-of asubstantially uniform film of U 0 which is sufiicientlythin so that there is a negligible absorption of alpha particles in -'the film. This thin film is deposited'onasuitablesupporting or backing member, such as'a diskof sheet pl'atinum or other noble metal, thereby constituting atargetwhich in turn'is supported upona copper' base -plate, -the-"wh0le then being employedin making the desired alphaactivity and. fission activity. measurements.

form.

The maximum thickness allowable for a film of U 0 is taken to be that thickness which corresponds to about 400 micrograms of uranium per square centimeter. In the case of a substantially uniform U 0 film of this thickness, approximately two to three percent of the alphaparticles originating within the film will be absorbed therein. Often in making isotopic analyses, substantially uniform U 0 films of thickness of the order. of magnitude corresponding to 40 micrograms of uranium per square centimeter are employed. Such a film absorbs only about 0.2 to 0.3% of the alpha'particles.

It may be noted that thin, uniform films of U 0 which are satisfactory for alpha activity measurements are also satisfactory for slow-neutron-produced fission measurements.

Inview of the foregoing, in the preparation of samples of uranium which are to be analyzed for their isotopic composition, it is necessary chemically to purify the uranium and then to deposit the uranium in a convenient chemical form as a thin film which has a uniform thickness correspondingto a density of less than about 400 micrograms of uranium per square centimeter. The parent application Serial No. 542,220 describes in detail a procedure for preparing a target of purified uranium for isotopic analysis, and contains claims directed to both theprocedure and the target so prepared. The present application claims a method for producing uranium of an extremely high degree of purity, suitable for isotopic analysis or otherwise.

Accordingly, it is an object of the invention to provide a method for obtaining uranium in an extremely pure Another object of the invention is to provide a method for preparing a sample of uranium of such purity that it may. be subjected to analysis for its uranium isotope content. I

A still further object of theinvention is to provide a :process for purifying a sample of uranium and obtaining the uranium so purified in the form .of a suitable uranium compound, such as U 0 vA further object of the invention is to provide a method for recovering uranium from the-collectors of an iso- Ltopesenriching device such as a calutron, andfor purifying-the uranium so recovered so that the isotopic composition ofthe uranium present in the collectors of the isotope enriching device may be determined.

Other objects and advantages of the inventionwill appear from the following detailed description, taken in conjunction with the accompanying drawings, in which .Figure; 1 is a diagrammatic floW sheet showing the initial steps in: the method, and Fig. 2 is a diagrammatic flow ,sheet showing further steps leading to theproductionof uranium in the form of a suitable compound, such as U 0 that has been substantially completely freed from associated impurities.

Referring now to Fig. 1, uranium Which has been deiposited on the collectors, taken for purposes of illustration to be constructed chiefly of copper, of an isotope enriching machine such as the calutron referred to above,

.isdissolved by giving the copper surfaces to which the uranium. has adhered an etching treatment with cold moderately concentrated nitric acid, e. g., 8 N. The solution. resulting from the nitric acid treatment contains uranium as uranyl ion, UO a considerable amount of copper as cupric ion, Cu++, the copperbeing present due to, partial solution of the collector, a little iron which may be present due to the fact that iron is sputtered into the collector from the steel calutron vacuum tank, a little .tinand lead from soft solder joints in the collector, a little silver and zinc from hard solder joints in the col- Jector, and insoluble material such as bits of graphite from carbon parts of the collector.

To the solution there i The filtrate contains all of the thecopper as complex filtered and .the precipitate, after being washed with a.

the'amount of ammonium produced.

added hydrochloric acid in an amount in excess of aces 285 that required to destroy all of the nitrate, and' their the solution is boiled, whereby nitric acid present is destroyed. to form NO and N and 'most of the excessHCl.is-re-- moved. By this treatment a hydrochlori c acid solutiom of the chlorides of the dissolved metals is formed, Tin}. although partially soluble in the solution, is largely present as 'a precipitate of metastannic acid, and'm'ost; of the silver is present as a precipitate of silver chloride... The solution is then filtered,- whereby silver chloride,

mctastannic acid and other insoluble-materials,inc1nd ing bits of carbon, are separated from'the solution. anti discarded. The filtrate, which contains the iron, copper, lead, and small amounts of-tin, zinc and. silver, is then treated with dilute carbon dioxide-free ammonium hydroxide, e. g., 6 N, whereby a precipitate:v comprising ammonium diuranate, lead hydroxide, anzdi iron hydroxide is formed, which contains traces-of silven,

' tin and copper, the amount of ammonium hydroxide bethat required for complete precipitation; zinc and practically all of The solution ising in excess of ammonio ions.

solution of carbon dioxide-free ammonium hydroxide is dissolved in concentrated hydrochloric acid and diluted so that the solution is about I to 2 N in hydrochloric acid. The solution, which contains uranium, lead, iron, and traces of silver, tin and copper, is saturated with hydrogen sulfide gas, whereby a precipitate of copper, silver, and tin sulfides is formed. The solution is filtered and the precipitate is discarded. The filtrate contains uranium, iron, lead, and a small amount of sulfur which has resulted from the oxidation of hydrogen sulfide.

The filtrate is then given further treatment, as outlined in Fig. 2. More particularly, the filtrate isevapor' rated to a. small volume to remove hydrogen sulfide and then concentrated nitric acid, e. g., N,.is added and the mixture is boiled, whereby hydrochloric acid in the solution is decomposed and any sulfur present is oxidized to sulfate, the amount of nitric acid required being. enough to oxidize all of the chloride and the sulfur present. Next, an approximately 2 /2% by weight ammonium carbonate solution in ide is added in excess to the solution, whereby a precipi. tate of ferric hydroxide and lead hydroxide is formed, carbonate solution in 3 N ammonium hydroxide added being in excess of that required for complete precipitation of the ferric hydroxide and the lead hydroxide. Uranium, which forms the complex ion UO (CO remains in solution. The solution is filtered and the precipitate is washed with an approximately 2 /z% by weight ammonium carbonate solution in 3 N ammonium hydroxide. The filtrate new contains uranium which has been substantially completely 'separated from metal impurities. The filtrate is acidified with concentrated nitric acid and concentrated by evaporation, whereby carbonate present is decomposed and carbon dioxide evolved. The resulting solution containing the uranium in the form of uranyl ion, UO is next evaporated to dryness and the residue is then ignited at'a dull red heat on a platinum disk, whereby uranium present is converted to U 0 There is found with it a certain amount of silica which results from a slight solution of the various glass vessels in which the above-described manipulations have taken place. The U 0 admixed with silica is then treated with concentrated nitric acid, whereby the U 0 is dissolved while the silica is left as an insoluble residue. The nitric acid solution of uranium is separated from the silica by filtering and the nitric acid solution is then placed in a tared platinum container and evaporated todryness, the residue then being ignited at a dull red heat, whereby pure U 0 is The pure U 0 produced in this manner is ready for use as such, or, if desired, it may be converted to-other uraniumg.

3 N ammonium hydroxmade therein.

- acid. is substantially 'solution', whereby insoluble impurities such as silver Serial No. 542,220, application those interested .10

. laim al 511 desired compounds of uranit m, for example uranyl nitrate,by' methods that may be known per se. One procedure for preparing it in the form of a thin uniform film of U 0 upon a noble metal l backing member, in which form it is eminently adapted for carrying out the isotopic analysis according to theaft )rementioned Segre-Kennedy procedure, is described in da :tail in the parent application previou tsly mentioned, and to which i are referred for further details \Vhile there has been de scribed what is at present considered to be the preferret' l embodiment of the invention, it"will be understood tha.1;;various modifications may be It will al sobe understood that the term uranium in the specification and claims, is used broadly to refer to substances comprising uranium without regard to its state of combination except as otherwise indicated by the context, It is intended to cover in the appended v 11' modifications as 'fall within the true spirit and" scope of the invention. I

. Wh at is claimed is 1'. The method'of i v 4 v urifying a sample of uranium com- 'prising'" ftreating'the sample with nitric acid, whereby uranium and metal impurities such as copper, iron, zinc, lyead', 'silver and tin" are put in solution, adding excess hydrochlorica'cid'and boiling the solution, whereby nitric -completely removed, filtering the chloride,

metastannic acid and'bits of carbon are removed ,frjbhithe solutijomprec ipitating the uranium in the solu- .tion 'jas'ammoniumfdiuifanate by adding ammonium hyidroxide, and filt'ermg, 'whereby uranium and impurities cad and iron along with traces of copper,'silver and'tiri'fareiseparated as a precipitate from impurities such if ammonio complex ions, a dilute hydrochloric acid, solution of uranium with impurities such as lead, iron,

as copper, 'zinc and silver which remain in solution as dissolving the precipitate to form o copper, silver and tin, saturatng the hydrochloric acid solution with H 5 and filtering,

whereby impurities such as copper, tin and silver are I removed 'fromthe solution, HQS" is "removed, adding h a whe yh nyi treating the solution I bon'ate ammonium wherebyfimpurities' such as iron and lead boiling the solution, whereby concentrated nitric acid and sulfur in the solution is oxidized, with an excess of ammonium carhydroxide reagent and filtering, are separated acidifying the 'ranium-which remains in solution,

I ,"solu on .with""nit'ric acid, evaporating the solution to a dry "residue, i'gni ting the residue at a red heat, whereby the uranium in the residue is converted to U 0 dissolving the U 03 in nitric acid and filtering the solution,

1 [whereby silica is separated from the solution, evaporating the solution and igniting the residue, whereby substantially pure U 0 is produced.

'2. The method of recovering uranium in substantially fpureform from metal surfaces comprising dissolving the uranium on the. said-surfaces withnitric acid, whereby uranium and metal impurities such as copper, iron, zinc,

J lead, silver and v tin ai'e put in solution, adding excess hydrochloric acid. and boiling the solution, whereby nitric acid .is substantially completely removed, filtering the f solution, whereby insoluble impurities such as silver chloride, metastannic-acidand bits of carbon are removed from the solution, precipitating the uranium in the solution as. ammonium diuranate ,dts sls and fil g such. as. lead andiron by adding ammonium hywhereby uranium and impurities V V I H v along with traces of copper, silver' and tinare separated as a precipitate from impurities I andsilver which remain in solution as ammonio complex ions, dissolving the precipitate to fprmadilutehydrochloric acid solution of uranium with j impuritiestsuch asrlead, iron, copper, silver and tin, MsatuIatingJhe hydrochloric acidsolution with H 8 and -:i'filtering,;iwhereby impurities. such as copper, tin and silver are removed fromthesolution, boiling the solution,

whereby H S is removed, adding concentrated nitric acid and heating, whereby any sulfur in the solution is oxidized, treating the solution with an excess of ammonium carbonate-ammonium hydroxide reagent and filtering, whereby impurities such as iron and lead are separated from uranium which remains in solution, acidifying the solution with nitric acid, evaporating the solution to a dry residue, igniting the residue at a red heat, whereby the uranium in the residue is converted to U 0 dissolving the U 0 in nitric acid and filtering the solution, whereby 10 silica is separated from the solution, evaporating the solution and igniting the residue, whereby substantially pure U 0 is produced.

References Cited in the file of this patent Mellor: Inorganic and Theoretical Chemistry, vol. 12, pages 32, 117, Longmans, London (1932).

Langes Handbook of Chemistry, 5th ed., page 1124, Handbook Publishers, Inc., Sandusky, Ohio (1944). 

2. THE METHOD OF RECOVERING URANIUM IN SUBSTANTIALLY PURE FORM FROM METAL SURFACES COMPRISING DISSOLVING THE URANIUM ON THE SAID SURFACES WITH NITRIC ACID, WHEREBY URANIUM AND METAL IMPURITIES SUCH AS COPPER, IRON, ZINC, LEAD, SILVER AND TIN ARE PUT IN SOLUTION, ADDING EXCESS HYDROCHLORIC ACID AND BOILING THE SOLUTION, WHEREBY NITRIC ACID IS SUBSTANTIALLY COMPLETELY REMOVED, FILTERING THE SOLUTION, WHEREBY INSOLUBLE IMPURTIES SUCH AS SILVER CHLORIDE, METASTANNIC ACID AND BITS OF CARBON ARE REMOVED FROM THE SOLUTION, PRECIPITATING THE URANIUM IN THE SOLUTION AS AMMONIUM DIURANATE BY ADDING AMMONIUM HYDROXIDE, AND FILTERING, WHEREBY URANIUM AND IMPURITIES SUCH AS LEAD AND IRON ALONG WITH TRACES OF COPPER, SILVER AND TIN ARE SEPARATED AS A PRECIPITATE FROM IMPURITIES SUCH AS COPPER, ZINC AND SILVER WHICH REMAIN IN SOLUTION AS AMMONIO COMPLEX IONS, DISSOLVING THE PRECIPITATE TO FORM A DILUTE HYDROCHLORIC ACID SOLUTION OF URANIUM WITH IMPURITIES SUCH AS LEAD, IRON, COPPER, SILVER AND TIN, SATURATING THE HYDROCHLORIC ACID SOLUTION WITH H2S AND FILTERING, WHEREBY IMPURITIES SUCH AS COPPER, TIN AND SILVER ARE REMOVED FROM THE SOLUTION, BOILING THE SOLUTION, WHEREBY H2S IS REMOVED, ADDING CONCENTRATED NITRIC ACID AND HEATING, WHEREBY ANY SULFUR IN THE SOLUTION IS OXIDIZED, TREATING THE SOLUTION WITH AN EXCESS OF AMMONIUM CARBONATE-AMMONIUM HYDROXIDE REAGENT AND FILTERING, WHEREBY IMPURITIES SUCH AS IRON AND LEAD ARE SEPARATED FROM URANIUM WHICH REMAINS IN SOLUTION, ACIDIFYING THE SOLUTION WITH NITRIC ACID, EVAPORATING THE SOLUTION TO A DRY RESIDUE, IGNITING THE RESIDUE AT A RED HEAT, WHEREBY THE URANIUM IN THE RESIDUE IS CONVERTED TO U3O8, DISSOLVING THE U3O8 IN NITRIC ACID AND FILTERING THE SOLUTION, WHEREBY SILICA IS SEPARATED FROM THE SOLUTION, EVAPORATING THE SOLUTION AND IGNITING THE RESIDUE, WHEREBY SUBSTANTIALLY PURE U3O8 IS PRODUCED. 